1. Field of the Invention
The invention relates to autoclaves for curing retreaded tires, that is, heat and pressure chambers for vulcanizing a material bonding a new tread to a used tire casing. More particularly, the invention is directed to an improvement in the heat transfer characteristics of an autoclave operating with forced-air flow.
2. Description of the Related Art
A type of autoclave in current use in the retread industry includes a chamber having an elongated, cylindrical shape capable of containing a group of tires for a curing process. The tires are encased in flexible covers or envelopes, which are evacuated to remove air from between and around the new tread and tire casing. The tires in the envelopes are suspended in the chamber to allow heated air to flow to the outer circumference of the tire and tread. The air in the autoclave is pressurized to force the new tread against the tire casing to achieve a uniform, tight bond. The air is heated to a temperature sufficient to produce the vulcanization reaction of the gum rubber layer interposed between the tread and casing.
A problem in the art exists in chambers that circulate air between the chamber and the heat source. The air returned to the chamber is heated to a sufficient temperature to vulcanize the entire group of tires in the chamber throughout the length of the chamber. Nonetheless, a “cold spot” can occur where the vulcanization reaction is less effective, between where the heated air enters the chamber from the supply duct and where the air is taken into the heat source. Often, the cold spot is at approximately the midpoint of the chamber.